1. Field
This disclosure relates generally to semiconductor devices, and more specifically, to determining aging-related damage for semiconductor devices.
2. Related Art
Semiconductor devices such as integrated circuits and printed circuit boards often perform several different functions to process data and interface with external components. The circuit design process often includes generating and testing a software model of a semiconductor device using Electronic Design Automation (EDA) tools. The EDA tools allow designers to prepare various views of components and interconnections between components that are included in a circuit. Models of the components can be used to simulate the performance of the circuit. Once the simulated model of the circuit is tested, files for other components in the design are converted to a gate-level description of the circuit(s). Placement and routing tools can be used on the gate-level descriptions to create a physical layout. The layout can be converted and stored in a format that is used by semiconductor foundries to manufacture the devices according to specifications.
The simulation can also take into account aging effects on some or all of the transistors that are included in a circuit. Incorporating the aging effects in the simulation allows designers to determine whether the circuit will still perform acceptably at or near the end of the expected life of the circuit. One aging effect in metal oxide semiconductor field effect transistors (MOSFETs) is known as bias temperature instability (BTI) that typically becomes a factor at high gate to source voltages (VGS). A high VGS creates a high vertical electric field across the gate channel, which leads to carriers (electrons or holes) in the transistor channel being pulled into the gate dielectric, thus damaging the gate dielectric. In high-k (where k is the dielectric constant of the material) metal gates, the damage may be proportional to the length and width of the channel. For digital circuits, BTI is more prevalent during static periods of operation than during switching.
Another aging effect is known as hot carrier injection (HCI) damage, which can occur when VGS is greater than threshold voltage (VT), with moderate to high drain source voltage (VDS). The high electric field at the drain causes impact ionization of current carriers. HCI damage is inversely proportional to channel length, and is more prevalent during switching than static operation in digital operation.